Method for treating wastewater containing heavy metals with used iron oxide catalyst

ABSTRACT

A method for treating a wastewater containing heavy metals with a used iron oxide catalyst is disclosed. The object of the present invention is to provide a method for treating a wastewater containing heavy metals with a used iron oxide catalyst in a manner that applies a strongly magnetic iron oxide catalyst used in the synthesis process of styrene monomer to a wastewater containing heavy metals such as metal plating wastewater or mine backwater to neutralize the wastewater and adsorb the heavy metals contained in the wastewater.  
     The present invention is to provide a method for treating a wastewater containing heavy metals using a used iron oxide catalyst, which is to treat an acidic wastewater having a pH value of about 1.0 and containing Cu, Fe, Ni, Cr or Zn, the method including: adding the used iron oxide catalyst containing magnetite (Fe 3 O 4 ) with at least 70% to the wastewater at a weight ratio of 1:0.05; stirring the wastewater mixed with the iron oxide catalyst at a speed of 60 rpm for 15 minutes in a stirrer; and subjecting the wastewater to solid-liquid separation using a magnet for adsorption and removal of the heavy metals.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for treating awastewater containing heavy metals with a used iron oxide catalyst. Moreparticularly, the present invention related to a method for treating awastewater containing heavy metals with an iron oxide catalyst, in whichthe heavy metals contained in the wastewater are adsorbed and removed bythe iron oxide catalyst used for synthesis of styrene monomer.

[0003] 2. Background of the Related Art

[0004] Styrene monomer used as a material of polymer in thepetrochemical industry is prepared from ethyl benzene in the presence ofan iron oxide catalyst, which uses ferric oxide (Fe₂O₃) as a principalmaterial and contains alkali metals and alkali earth metals in order toenhance its catalytic activity. The synthesis of styrene monomer usingthe iron oxide catalyst involves a dehydrogenation reaction in whichhydrogen is generated to reduce ferric oxide (Fe₂O₃) to magnetite(Fe₃O₄). So the lifetime of the catalyst is normally no more than one ortwo years.

[0005] The used iron oxide catalyst is handed over to a special wastetreatment agent and buried in the ground at a treatment expense. Morethan about 70 percents of the used catalyst is magnetite (Fe₃O₄).

[0006] In the treatment of a wastewater containing heavy metals such asmetal plating wastewater or mine backwater, the suspended materials aredirectly subjected to solid-liquid separation. But the elimination ofthe heavy metals from the wastewater involves conversion of the heavymetals to cations susceptible to precipitation by oxidation orreduction; neutralization of heavy metal cations and precipitation bydouble decomposition; adsorption (mercury); ion-exchange method; orreverse osmosis. The widely used method is to neutralization-precipitatethe wastewater containing heavy metals with calcium hydroxide (hydratedlime).

[0007] However, the neutralization-precipitation of the wastewater withcalcium hydroxide produces sludge after filtration and requires it to beburied as a Class 2 waste. The sludge containing water by more than 80percents is of great bulk and generates seepage water when buried in theground, thereby causing environmental problems such as soilcontamination and increasing the expense for wastewater treatment.

SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention is directed to a method fortreating a wastewater containing heavy metals with a used iron oxidecatalyst that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

[0009] An object of the present invention is to provide a method fortreating a wastewater containing heavy metals with a used iron oxidecatalyst in a manner that applies a strongly magnetic iron oxidecatalyst used in the synthesis process of styrene monomer to awastewater containing heavy metals such as metal plating wastewater ormine backwater to neutralize the wastewater and adsorb the heavy metalscontained in the wastewater.

[0010] Additional advantages, objects, and features of the inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof.

[0011] To achieve these objects and other advantages and in accordancewith the purpose of the invention, as embodied and broadly describedherein, a method for treating a wastewater containing heavy metals usinga used iron oxide catalyst, which is to treat an acidic wastewaterhaving a pH value of about 1.0 and containing Cu, Fe, Ni, Cr or Zn,includes: (a) adding the used iron oxide catalyst containing magnetite(Fe₃O₄) with at least 70% to the wastewater at a weight ratio of 1:0.05;(b) stirring the wastewater mixed with the iron oxide catalyst at aspeed of 60 rpm for 15 minutes in a stirrer; and (c) subjecting thewastewater to solid-liquid separation using a magnet for adsorption andremoval of the heavy metals.

[0012] The present invention is to adsorb/eliminate heavy metalscontained in the wastewater, such as Cu, Fe, Ni, Cr or Zn using a usediron oxide catalyst and includes adding the used iron oxide catalyst tothe wastewater at a predetermined weight ratio, stirring the mixture andsubjecting the wastewater to solid-liquid separation using a magnet.

[0013] The iron oxide catalyst is a special waste to be buried in theground after its use in the preparation of styrene monomer from ethylbenzene and contains magnetite (Fe₃O₄) with 70 percents and additionallyalkali metals and alkali earth metals. The alkali metals and the alkaliearth metals contained in the used catalyst are very soluble in water toshow a strong alkalinity and thus neutralize an acidic wastewater suchas metal plating wastewater or mine backwater. Also the iron oxideparticles such as Fe₂O₃ or Fe₃O₄ adsorb heavy metals.

[0014] Namely, the used iron oxide catalyst containing magnetite (Fe₃O₄)as a principal component is so strongly magnetic as to adsorb heavymetal ions precipitated in the neutral state and to allow solid-liquidseparation of the wastewater, thereby neutralizing the wastewater withthe alkali metals and the alkali earth metals.

[0015] Accordingly, the present invention involves adding, based on thetotal weight of the wastewater, 5 wt. % of a used iron oxide catalystpowder to the wastewater containing Cu, Fe, Ni, Cr or Zn, stirring themixture at 60 rpm for about 15 minutes and subjecting the wastewater tosolid-liquid separation using a magnet.

[0016] It is to be understood that both the foregoing generaldescription and the following detailed description of the presentinvention are exemplary and explanatory and are intended to providefurther explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Reference will now be made in detail to the preferred embodimentsof the present invention.

EXAMPLE 1

[0018]

[0019] Synthetic wastewater containing each 200 mg/l of Cu, Fe, Ni, Cror Zn ion were prepared, and each 1 l of them were controlled to have apH value of 1.0 to 2.0. Adding 50 g of a used iron oxide catalyst toeach synthetic wastewater of a predetermined pH value, the mixture wasstirred at 60 rpm for 15 minutes with a stirrer and removed of sludgewith a magnet. The filtrate was collected to analyze the content of eachheavy metal. The results are presented in Table 1. TABLE 1 Cu Fe Ni ZnTotal Cr Concentration (mg/l) of 0.05 0.10 0.01 0.02 0.02 Filtrate AfterTreatment Removal Rate (%) 99.97 99.95 99.99 99.99 99.99

EXAMPLE 2

[0020] Synthetic wastewater containing each 500 mg/l of Cu, Fe, Ni, Cror Zn ion were prepared, and each 1 l of them were controlled to have apH value of 1.0 to 2.0. Adding 50 g of a used iron oxide catalyst toeach synthetic wastewater of a predetermined pH value, the mixture wasstirred at 60 rpm for 15 minutes with a stirrer and removed of sludgewith a magnet. The filtrate was collected to analyze the content of eachheavy metal. The results are presented in Table 2. TABLE 2 Cu Fe Ni ZnTotal Cr Concentration (mg/l) of 0.10 0.10 0.05 0.10 0.05 Filtrate AfterTreatment Removal Rate (%) 99.98 99.98 99.99 99.98 99.99

EXAMPLE 3

[0021] Calcium hydroxide used as a heavy metal precipitator was added to1 l of a synthetic wastewater containing 200 mg/l of Zn ion and having apH value of 2.0 to control the pH value of the wastewater to 10.0. Thewastewater was added to a 1 l cylinder and measure in regard to thevolume and the sedimentation velocity of the sludge. The water contentof the sludge was also measured. On the other hand, 50 g of a used ironoxide catalyst was added to 1 l of a synthetic wastewater containing 200mg/l of Zn ion and having a pH value of 2.0. The mixture was stirred for15 minutes and added to a 11 cylinder. Subsequently, the volume and thesedimentation velocity of the sludge were measured and compared withthose of the sludge in the wastewater treated with calcium hydroxide.The results are presented in Table 3. TABLE 3 Used Iron Calcium OxideType of Heavy Metal Remover Hydroxide Catalyst Volume of Sludge (cm³)125 39 Water Content of Sludge (%) 81 27 Sedimentation Velocity ofSludge 275 250 (cm³/min) Sedimentation Velocity of Sludge When 275 420Using Magnet (cm³/min)

[0022] The forgoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teachings canbe readily applied to other types of apparatuses. The description of thepresent invention is intended to be illustrative, and not to limit thescope of the claims. Many alternatives, modifications, and variationswill be apparent to those skilled in the art.

[0023] As described above, the present invention applies an iron oxidecatalyst used in the synthesis of styrene monomer to an acidicwastewater containing heavy metals to adsorb the heavy metals, with astrong recycling effect, and uses a magnet instead of performingfiltration to shorten the time for solid-liquid separation and, comparedwith the case of using calcium hydroxide as a precipitator, to reducethe volume and the water content of the precipitate of the heavy metalions, i.e., sludge, thereby lowering the expense of sludge re-treatment.

What is claimed is:
 1. A method for treating a wastewater containingheavy metals using a used iron oxide catalyst, which is to treat anacidic wastewater having a pH value of about 1.0 and containing Cu, Fe,Ni, Cr or Zn, the method comprising: adding the used iron oxide catalystcontaining magnetite (Fe₃O₄) with at least 70% to the wastewater at aweight ratio of 1:0.05; stirring the wastewater mixed with the ironoxide catalyst at a speed of 60 rpm for 15 minutes in a stirrer; andsubjecting the wastewater to solid-liquid separation using a magnet foradsorption and removal of the heavy metals.